I'm guessin that one of the major issues is that you're not used to tight, clean, accurate bass. I've read a few reviews of the JBL G400's and their bass is quite often referred to as "big", "boomy", "slow"...

Going from that to the M80ti's is going to be a dramatic change. You're ears are accustomed to a big huge punch in the chest from the JBL's over-the-top boomy bass.